Board Thread:Pokémon Help/@comment-34515084-20180225105459/@comment-27248965-20180225110300

PBB is in Sun/Moon settings and hasn't been updated to US/UM yet, but yes, Pichu is supposed to learn Nasty Plot at Lv. 13. There is a bug of Pokemon not learning attacks if levelling up too fast (say, from Lv. 1 all the way to Lv. 15 after defeating 1 Pokemon), is it the case of your Pichu?